This project will continue the previous effects of hepatitis C virus (HCV) proteins on host function. Previous efforts have demonstrated that HCV envelope protein E2 can inhibit cellular protein kinase PKR, thus interfering with the effects of interferon. Furthermore, NS5a protein can interact with several cellular proteins, either directly or indirectly interfering with the actions of interferon and also affecting other cellular functions. In this project period, this laboratory will concentrate on the potential effects of these viral proteins on interferon activities in the context of full-length viral polyproteins. First, inducible liver-derived cell lines expressing the full-length HCV proteins will be established. These cell lines will then be used to perform the following studies: 1) Investigation of the effects of HCV polyproteins on PKR activities, including PKR phosphorylation, translation activities and NfkappaB activation, and their possible effects on apoptosis and tumor formation. The effects of these viral proteins will be compared with the effects of expression of E2 or NS5a proteins alone. 2) Characterization of HCV proteins on the antiviral effects of interferon, including the effects on the inhibition of encephalomyocarditis virus or vesicular stomatitis virus replication and interferon-induced effector proteins, such as MHC class I protein. 3) Exploration of other potential effects of NS5a on host functions, with emphasis on the effects on the FK506-binding proteins and vesicle transport proteins (VAP proteins). These projects are expected to contribute to the understanding of the mechanism of HCV resistance to interferon and to the improvement of interferon therapy in the future.